Many prior attempts have been made to design embrittlement freezers using cryogenic liquids in order to cool metallic, rubber and plastic materials below their embrittlement temperature. The embrittled material is fragmented in various types of impact mills in order to recover and recycle valuable components of the embrittled waste materials. One such cryogenic freezer is disclosed in U.S. Pat. No. 3,914,953 which is particularly designed for embrittling large metallic objects such as motors, transformers and scrap automobile bodies. At the same time, numerous cryogenic freezers have been designed for freezing food products such as the freezer designs disclosed in U.S. Pat. Nos. 3,531,946 and 3,022,636. In such cryogenic freezers, there has been a persistent problem in effectively sealing the ends of tunnel-type freezers, and particularly the discharge end, against the loss of cold refrigerant gas and the entrance of warm, moist ambient air. A large number of solutions have been proposed to solve this problem including air and gas curtains such as disclosed in U.S. Pat. Nos. 3,531,946 and 3,914,953. In addition, various types of gas locks have been attempted including star-wheels, and those formed between flexible curtains, rotating brushes, and sliding or pivoted doors as taught, for example, in U.S. Pat. Nos. 2,951,353; 3,048,989; 3,090,134; and 3,022,636. While the prior designs of gas locks may be partially effective in food freezers where the products are small and uniform in shape such that the entrance and discharge openings are quite small and not subject to jamming, the use of gas locks has not been efficient, particularly in the large type of cryogenic freezers which are required for embrittling large articles of non-uniform size or shape as described above. In addition, a freezer designed particularly for use in embrittling large pieces or strips of automobile and truck tires presents additional problems due to the totally irregular shapes of the pieces being cooled which not only require a large gas space within the gas lock, but also tend to jam the locks whenever an unusually large piece is encountered.
The present invention solves this long-standing problem of effectively sealing both ends of a large, embrittlement freezer which is particularly designed for embrittling random size pieces of scrap tires.